The invention relates to a seat adjuster, for example, for adjusting the height of a seat or the tilting of the backrest of the seat in a motor vehicle.
Known are seat adjusters with a locking mechanism through which the adjustable part of the seat can be tightly locked onto a stationary part. If the user desires to adjust the seating position, the locking mechanism has to, first, be unlocked before the adjustable part of the seat can be adjusted either through direct bodily influence on the adjustable part or, however, with the aid of an adjusting device such as a hand wheel or lever or the like. When the desired new position is reached, the locking mechanism is allowed to reengage in this position.
Seat adjusters of this type, however, have the disadvantage that only a stepwise adjustment, according to measure of the discrete engagement positions of the locking mechanism, is possible. Besides this, convenience of operation is impaired because the locking mechanism is difficult to release especially while under a load and can easily get stuck or jammed during re-engagement in the new position and/or abruptly falls into the engagement position accompanied by an unpleasant noise. Further, such a locking mechanism is difficult to combine with a drive which increases the operational force exerted by hand onto the adjusting device.
On the other hand, known are seat adjusters which, instead of a locking mechanism, have brake acting between the adjustable part and the stationary part with which the adjustable part can be steplessly blocked at selected positions in both directions. To release the brake, a releasing device which is coupled to the adjusting device is provided such that the brake is released automatically when the adjusting device is operated and the force is transferred from the adjusting device to the adjustable part, while, if the adjusting device is not operated and there is a flow of force in the opposite direction, the brake is automatically blocked.
Seat adjusters of this type make possible a stepless adjustment of the seat and are excellent in operational convenience since the release of the brake during operation of the adjusting device as well as the gripping of the brake after reaching the desired position of engagement occur automatically and in a manner hardly noticeable by the user.
In seat adjusters of this latter type, a load acting in the same direction over a longer period of time can lead to a crawling of the brake and thus to a gradual, undesirable adjustment of the seat, especially when, in addition to the continuously acting force, there is a vibration such as is regularly the case in motor vehicles during driving. For example, in seat height adjusters, there is often a strong spring which places an upward pressure on the seat and thus partially balances out the body weight of the user, such that the force required for an adjustment process is reduced. If the seat is occupied, the downwardly acting force of the weight outweigh, such that the seat gradually slopes downward due to the crawling effect of the brake. If the seat has no load, however, the upwardly directed force of the spring outweighs, such that the seat moves gradually upward. In both cases, from time to time, a readjustment of the seating position is needed.
It is an object of the invention to provide a stepless seat adjuster in which the seat remains reliably in the set position even under a load.